This application is based upon and claims benefit of priority of Japanese Patent Application No. 2000-373758 filed on Dec. 8, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a starter motor having an intermediate gear, in which a rotational torque of an output shaft of a motor is transferred to an internal combustion engine through an intermediate gear.
2. Description of Related Art
An example of the starter motors of this kind is disclosed in JP-U-50-91643. The intermediate gear structure disclosed in this publication is briefly shown in FIGS. 4A and 4B attached to this specification. As shown in FIG. 4A, an intermediate shaft 110 is disposed in parallel to an output shaft 100 of a motor. The intermediate shaft 110 rotatably supports an intermediate gear 130 that engages with a pinion 120 supported on the output shaft 100 and rotated by the motor. A coupler 140 that connects the pinion 120 to the intermediate gear 130 to slidably drive the intermediate gear 130 in an axial direction of the intermediate shaft 110 together with the pinion 120 is disposed in circular grooves 121, 131 formed on both the pinion 120 and the intermediate gear 130.
To start up the internal combustion engine, the pinion 120 is shifted rightward in FIG. 4A, and the intermediate gear 130 is also shifted rightward together with the pinion 120, thereby engaging with a ring gear 150 of the engine. The rotational torque of the motor is transferred to the ring gear 150 of the engine through the pinion 120 and the intermediate gear 130. When the pinion 120 and the intermediate gear 130 rotate, the coupler 140 does not rotate because its arcuate arms 141, 142 (shown in FIG. 4B) stay in the circular grooves 121, 131, respectively.
However, in the conventional structure, there has been a problem in assembling the intermediate gear 130 to the pinion 120. The coupler 140 easily drops off from the circular grooves 121, 131 in the assembling process because it is only loosely positioned in the circular grooves. Accordingly, it has been difficult to keep the coupler 140 in the position in the assembling process. Further, there has been another problem that it is difficult to give a sufficient mechanical strength to the coupler 140 because it must be positioned in thin circular grooves 121, 131 formed on the pinion 120 and the intermediate gear 130. Especially, it has been difficult to secure a sufficient bending strength of the coupler 140, because the coupler 140 must be made thin to be accommodated in the circular grooves 121, 131.
The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved starter motor having an intermediate gear, in which a pinion and the intermediate gear is coupled with an easily mountable retainer having a sufficient mechanical strength.
A starter motor for cranking an internal combustion engine includes a pinion driven by an electrical motor and an intermediate gear engaged with the pinion. The intermediate gear engages with a ring gear of the internal combustion engine to crank up the engine. The pinion is slidably and rotatably supported on an output shaft of the motor, while the intermediate gear is slidably and rotatably supported on an intermediate shaft disposed in parallel to the output shaft. The pinion and the intermediate gear are coupled with a retainer, so that the intermediate gear is shifted in its axial direction together with the pinion when the pinion is shifted to crank up the engine.
The retainer has a first groove engaging with a pinion boss formed integrally with the pinion and a second groove positioned to partly cover an outer periphery of a cylindrical boss formed integrally with the intermediate gear. The first groove has a resilient opening, a width of which is smaller than a diameter of the pinion boss. To connect the retainer to the pinion boss, the resilient opening is forcibly opened and recovers its original position after the retainer is connected to the pinion boss. Since the retainer is connected to the pinion boss in this manner, the retainer is prevented from dropping off during a process of assembling the intermediate gear to the starter motor. The positions of the first and the second grooves of the retainer may be reversed so that the retainer engages with the cylindrical boss of the intermediate gear in place of the pinion boss. Since the retainer is positioned outside the pinion boss and the cylindrical boss of the intermediate gear, the retainer can be made thick enough to secure a sufficient mechanical strength.
The retainer coupling the pinion and the intermediate gear does not rotate, while components contacting the retainer rotate. Convex surfaces are formed on the side surfaces of the retainer contacting the rotating components to alleviate friction between the retainer and the components.
According to the present invention, the retainer having a sufficient mechanical strength can be easily mounted on the starter motor without disturbing the assembling process. Further, friction between the retainer and rotating components is effectively alleviated.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.